Deep Sky Remote Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Deep Sky Remote Observatory clear sky chart from 2005-11-06 to 2026-10-14.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	3 5% 2 5% 4 4 4 4 6% 7% 57%	157443
	Night	4 6% 2 5% 3 3 4 3 5% 7% 57%	151913
Transparency	Day	24% 4 10% 21% 26% 15%	152323
	Night	26% 4 9% 20% 25% 16%	148040
Seeing	Day	9% 13% 27% 31% 16% 4	17692
	Night	8% 6% 23% 37% 21% 3	27875

By Month

Percentage Cloud Cover SW (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	5% 10% 3 6% 4 3 4 3 5% 6% 51%	5318
	11th to 20th	Day	3 5% 1 4 3 3 3 2 3 5% 67%	5340
	21st to end	Day	4 8% 2 6% 3 3 3 3 4 5% 59%	5844
February	1st to 10th	Day	4 10% 3 6% 5% 3 3 3 5% 6% 52%	1890
	11th to 20th	Day	5% 12% 3 7% 5% 4 4 3 4 6% 47%	1850
	21st to end	Day	5% 14% 3 6% 4 3 2 3 3 5% 52%	1803
March	1st to 10th	Day	4 9% 2 5% 3 4 4 3 5% 7% 51%	5064
	11th to 20th	Day	3 11% 5% 11% 5% 5% 5% 4 6% 7% 39%	5110
	21st to end	Day	5% 10% 3 7% 5% 5% 5% 4 6% 8% 42%	5607
April	1st to 10th	Day	5% 7% 2 6% 5% 4 4 4 5% 7% 53%	2476
	11th to 20th	Day	4 6% 2 5% 5% 4 6% 4 6% 7% 52%	2491
	21st to end	Day	5% 6% 1 5% 4 4 4 4 6% 7% 54%	2520
May	1st to 10th	Day	3 4 2 6% 4 5% 5% 5% 6% 8% 52%	7602
	11th to 20th	Day	3 3 1 3 3 3 4 4 6% 7% 61%	7596
	21st to end	Day	2 2 1 3 3 3 4 3 5% 7% 67%	8610
June	1st to 10th	Day	3 3 1 3 3 3 3 3 5% 8% 64%	2940
	11th to 20th	Day	2 2 1 3 2 2 3 2 4 5% 73%	2940
	21st to end	Day	1 2 1 3 3 3 4 4 6% 6% 66%	2932
July	1st to 10th	Day	1 1 1 2 3 3 3 3 5% 5% 73%	7649
	11th to 20th	Day	1 2 1 5% 4 6% 7% 6% 9% 10% 49%	7650
	21st to end	Day	2 2 1 4 3 4 5% 4 8% 11% 56%	8304
August	1st to 10th	Day	2 2 1 4 4 4 5% 5% 7% 10% 56%	7549
	11th to 20th	Day	2 2 1 4 4 4 5% 5% 6% 9% 57%	7435
	21st to end	Day	2 4 1 5% 5% 5% 7% 6% 9% 11% 44%	7751
September	1st to 10th	Day	6% 3 1 5% 4 4 4 3 6% 7% 55%	2520
	11th to 20th	Day	4 4 2 5% 5% 4 5% 4 6% 6% 56%	2426
	21st to end	Day	6% 3 1 4 3 3 3 3 4 6% 64%	2258
October	1st to 10th	Day	5% 2 1 3 2 2 2 2 3 4 74%	3370
	11th to 20th	Day	5% 4 2 5% 4 4 4 3 6% 6% 56%	3280
	21st to end	Day	5% 4 1 3 2 3 3 3 4 5% 67%	3548
November	1st to 10th	Day	3 3 1 3 3 2 3 3 4 7% 67%	2059
	11th to 20th	Day	4 4 1 3 2 2 3 2 4 6% 68%	1927
	21st to end	Day	5% 7% 2 6% 3 2 3 3 3 4 61%	1680
December	1st to 10th	Day	4 5% 2 3 3 2 2 2 4 7% 66%	2700
	11th to 20th	Day	5% 7% 2 4 3 3 3 3 5% 8% 56%	3106
	21st to end	Day	5% 10% 3 6% 3 3 3 3 4 6% 56%	4298
January	1st to 10th	Night	5% 9% 4 9% 4 4 4 3 4 5% 49%	7605
	11th to 20th	Night	3 7% 2 4 2 2 3 2 3 5% 67%	7650
	21st to end	Night	5% 10% 3 5% 3 2 2 2 4 6% 59%	8370
February	1st to 10th	Night	4 9% 3 5% 3 3 3 3 4 6% 59%	2730
	11th to 20th	Night	7% 10% 3 6% 3 4 4 3 4 6% 52%	2655
	21st to end	Night	6% 10% 3 5% 4 2 3 3 4 6% 53%	1997
March	1st to 10th	Night	5% 11% 3 6% 3 3 4 3 5% 5% 51%	5050
	11th to 20th	Night	5% 11% 4 6% 4 4 4 4 5% 7% 46%	5110
	21st to end	Night	5% 11% 3 7% 4 4 4 4 6% 7% 47%	5610
April	1st to 10th	Night	8% 7% 2 4 4 3 4 4 5% 6% 53%	2142
	11th to 20th	Night	7% 6% 2 6% 3 4 4 4 5% 5% 54%	2077
	21st to end	Night	5% 6% 2 5% 4 3 4 3 4 6% 59%	2100
May	1st to 10th	Night	4 4 2 4 4 4 4 4 6% 7% 57%	5329
	11th to 20th	Night	4 5% 2 4 3 3 4 3 5% 7% 59%	5296
	21st to end	Night	3 3 1 3 2 2 3 3 4 6% 69%	5579
June	1st to 10th	Night	2 2 1 3 2 2 4 3 5% 7% 67%	1680
	11th to 20th	Night	3 3 1 3 2 2 2 2 4 5% 72%	1680
	21st to end	Night	2 2 1 3 3 3 4 4 7% 7% 65%	1681
July	1st to 10th	Night	2 2 1 4 3 3 3 3 5% 6% 67%	5340
	11th to 20th	Night	2 3 2 6% 5% 5% 6% 6% 8% 11% 46%	5340
	21st to end	Night	2 3 1 5% 4 5% 5% 5% 9% 12% 47%	5805
August	1st to 10th	Night	1 2 1 5% 4 4 6% 5% 7% 10% 53%	5273
	11th to 20th	Night	2 3 1 5% 4 4 5% 5% 7% 10% 54%	5418
	21st to end	Night	4 5% 2 6% 5% 6% 7% 6% 9% 12% 39%	6465
September	1st to 10th	Night	4 4 1 5% 5% 5% 6% 4 6% 7% 53%	2100
	11th to 20th	Night	4 4 1 5% 4 5% 4 3 5% 6% 59%	2189
	21st to end	Night	6% 4 1 4 2 2 2 2 3 5% 67%	2360
October	1st to 10th	Night	4 3 1 2 2 2 2 2 3 5% 75%	4040
	11th to 20th	Night	6% 5% 2 6% 5% 5% 4 3 5% 5% 55%	3934
	21st to end	Night	5% 5% 2 4 2 2 2 2 3 4 69%	4252
November	1st to 10th	Night	5% 4 1 3 3 2 3 3 4 6% 67%	2460
	11th to 20th	Night	5% 5% 1 3 2 2 3 2 3 5% 70%	2662
	21st to end	Night	5% 8% 2 4 3 2 2 3 4 6% 62%	2940
December	1st to 10th	Night	4 5% 1 2 2 2 2 2 3 6% 71%	4710
	11th to 20th	Night	5% 8% 2 5% 3 3 3 2 5% 7% 57%	5321
	21st to end	Night	6% 10% 2 5% 3 3 2 2 3 5% 59%	6963

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	34% 3 14% 29% 18% 2	5321
	11th to 20th	Day	20% 4 10% 22% 29% 14%	5340
	21st to end	Day	29% 3 5% 21% 32% 9%	5844
February	1st to 10th	Day	33% 4 12% 22% 21% 8%	1890
	11th to 20th	Day	39% 5% 8% 21% 22% 6%	1859
	21st to end	Day	35% 4 7% 18% 29% 8%	1803
March	1st to 10th	Day	28% 7% 7% 20% 32% 8%	5064
	11th to 20th	Day	39% 8% 10% 22% 16% 5%	5110
	21st to end	Day	35% 7% 10% 23% 23% 2	5607
April	1st to 10th	Day	29% 5% 8% 18% 27% 12%	2476
	11th to 20th	Day	29% 6% 9% 18% 27% 12%	2494
	21st to end	Day	26% 6% 9% 21% 30% 9%	2520
May	1st to 10th	Day	27% 4 10% 22% 26% 11%	7602
	11th to 20th	Day	18% 5% 7% 18% 38% 15%	7599
	21st to end	Day	15% 3 6% 18% 41% 17%	8611
June	1st to 10th	Day	17% 5% 7% 17% 31% 23%	2940
	11th to 20th	Day	14% 3 5% 11% 24% 43%	2940
	21st to end	Day	14% 5% 7% 14% 23% 37%	2932
July	1st to 10th	Day	13% 3 6% 7% 14% 58%	7586
	11th to 20th	Day	26% 4 13% 23% 21% 13%	7581
	21st to end	Day	19% 5% 16% 26% 18% 16%	8120
August	1st to 10th	Day	26% 4 16% 14% 19% 20%	5978
	11th to 20th	Day	25% 4 16% 23% 19% 13%	5858
	21st to end	Day	29% 5% 14% 26% 18% 8%	6078
September	1st to 10th	Day	26% 6% 9% 17% 23% 19%	2520
	11th to 20th	Day	25% 8% 9% 15% 21% 22%	2426
	21st to end	Day	22% 3 7% 15% 34% 19%	2258
October	1st to 10th	Day	16% 3 5% 12% 32% 32%	3370
	11th to 20th	Day	27% 3 5% 21% 32% 13%	3280
	21st to end	Day	20% 3 5% 23% 42% 7%	3548
November	1st to 10th	Day	18% 3 9% 26% 37% 8%	2059
	11th to 20th	Day	19% 3 8% 28% 34% 8%	1927
	21st to end	Day	28% 4 8% 25% 25% 11%	1680
December	1st to 10th	Day	20% 4 9% 35% 28% 5%	2700
	11th to 20th	Day	28% 5% 7% 33% 25% 2	3104
	21st to end	Day	30% 4 12% 22% 22% 8%	4298
January	1st to 10th	Night	37% 4 11% 26% 19% 4	7605
	11th to 20th	Night	19% 4 11% 23% 28% 14%	7650
	21st to end	Night	29% 4 5% 21% 28% 14%	8370
February	1st to 10th	Night	27% 4 12% 23% 25% 9%	2730
	11th to 20th	Night	34% 4 9% 22% 25% 7%	2656
	21st to end	Night	31% 4 8% 18% 28% 10%	1997
March	1st to 10th	Night	29% 6% 6% 18% 31% 10%	5050
	11th to 20th	Night	35% 7% 8% 20% 23% 7%	5110
	21st to end	Night	33% 7% 9% 26% 22% 4	5610
April	1st to 10th	Night	31% 5% 7% 19% 27% 12%	2142
	11th to 20th	Night	30% 4 7% 17% 27% 14%	2077
	21st to end	Night	26% 4 7% 18% 34% 11%	2100
May	1st to 10th	Night	24% 4 10% 22% 31% 9%	5327
	11th to 20th	Night	22% 5% 7% 16% 33% 17%	5297
	21st to end	Night	17% 3 5% 15% 39% 22%	5580
June	1st to 10th	Night	15% 4 8% 14% 29% 30%	1680
	11th to 20th	Night	15% 4 6% 11% 19% 45%	1680
	21st to end	Night	15% 5% 8% 13% 21% 38%	1681
July	1st to 10th	Night	17% 4 5% 7% 10% 55%	5295
	11th to 20th	Night	29% 5% 13% 21% 15% 18%	5286
	21st to end	Night	27% 5% 16% 23% 13% 16%	5677
August	1st to 10th	Night	27% 5% 14% 12% 14% 29%	4168
	11th to 20th	Night	28% 4 17% 21% 14% 16%	4271
	21st to end	Night	30% 4 14% 27% 15% 10%	5069
September	1st to 10th	Night	27% 7% 10% 14% 19% 23%	2100
	11th to 20th	Night	25% 6% 8% 16% 20% 25%	2189
	21st to end	Night	22% 3 6% 14% 30% 25%	2360
October	1st to 10th	Night	15% 3 5% 11% 27% 39%	4040
	11th to 20th	Night	31% 3 5% 13% 34% 14%	3934
	21st to end	Night	20% 3 4 19% 42% 12%	4252
November	1st to 10th	Night	19% 3 7% 22% 36% 13%	2460
	11th to 20th	Night	18% 4 6% 25% 37% 10%	2662
	21st to end	Night	25% 3 7% 22% 29% 14%	2940
December	1st to 10th	Night	18% 2 7% 38% 26% 9%	4710
	11th to 20th	Night	27% 4 6% 30% 30% 3	5322
	21st to end	Night	30% 3 10% 24% 24% 9%	6963

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	19% 12% 33% 25% 10% 1	330
	11th to 20th	Day	14% 16% 31% 26% 12% 1	330
	21st to end	Day	10% 14% 34% 29% 11% 2	363
February	1st to 10th	Day	11% 18% 37% 26% 7% 2	330
	11th to 20th	Day	16% 19% 37% 22% 7%	330
	21st to end	Day	12% 21% 41% 18% 8%	346
March	1st to 10th	Day	15% 21% 31% 24% 9%	540
	11th to 20th	Day	14% 21% 33% 22% 8% 2	540
	21st to end	Day	15% 27% 36% 14% 7% 1	594
April	1st to 10th	Day	12% 23% 31% 23% 9% 2	540
	11th to 20th	Day	15% 25% 33% 18% 6% 2	532
	21st to end	Day	11% 24% 33% 23% 8% 1	540
May	1st to 10th	Day	11% 20% 37% 24% 7% 1	543
	11th to 20th	Day	8% 16% 33% 27% 14% 3	568
	21st to end	Day	8% 17% 30% 25% 15% 5%	701
June	1st to 10th	Day	6% 8% 24% 38% 22% 3	780
	11th to 20th	Day	4 9% 26% 38% 18% 5%	780
	21st to end	Day	3 7% 28% 40% 17% 5%	772
July	1st to 10th	Day	3 2 19% 44% 25% 7%	566
	11th to 20th	Day	3 2 12% 39% 32% 12%	564
	21st to end	Day	5% 1 13% 41% 30% 9%	619
August	1st to 10th	Day	5% 3 18% 43% 26% 6%	567
	11th to 20th	Day	4 3 20% 38% 26% 10%	557
	21st to end	Day	4 1 21% 40% 27% 6%	627
September	1st to 10th	Day	6% 2 23% 38% 25% 6%	570
	11th to 20th	Day	5% 8% 28% 38% 17% 4	570
	21st to end	Day	9% 10% 23% 32% 21% 5%	518
October	1st to 10th	Day	10% 14% 21% 23% 21% 10%	360
	11th to 20th	Day	12% 13% 27% 27% 17% 4	339
	21st to end	Day	11% 15% 21% 32% 18% 3	363
November	1st to 10th	Day	10% 13% 28% 29% 17% 3	330
	11th to 20th	Day	8% 12% 32% 31% 15% 3	330
	21st to end	Day	12% 14% 27% 33% 12% 2	330
December	1st to 10th	Day	11% 10% 31% 31% 15% 3	330
	11th to 20th	Day	10% 14% 31% 25% 16% 4	330
	21st to end	Day	19% 15% 29% 29% 8% 1	363
January	1st to 10th	Night	11% 5% 27% 37% 16% 4	840
	11th to 20th	Night	9% 7% 29% 35% 17% 3	840
	21st to end	Night	11% 7% 31% 33% 14% 3	924
February	1st to 10th	Night	10% 7% 34% 35% 12% 2	840
	11th to 20th	Night	11% 9% 36% 33% 10% 1	824
	21st to end	Night	13% 8% 34% 36% 9%	692
March	1st to 10th	Night	11% 9% 32% 34% 13% 2	840
	11th to 20th	Night	8% 9% 29% 33% 18% 2	840
	21st to end	Night	12% 11% 27% 36% 14% 1	924
April	1st to 10th	Night	12% 11% 29% 40% 8% 1	672
	11th to 20th	Night	10% 16% 26% 35% 12% 1	623
	21st to end	Night	9% 11% 32% 35% 11% 1	630
May	1st to 10th	Night	8% 9% 26% 42% 14% 1	630
	11th to 20th	Night	9% 5% 25% 39% 19% 4	621
	21st to end	Night	8% 11% 23% 35% 20% 3	683
June	1st to 10th	Night	2 5% 19% 46% 27% 1	630
	11th to 20th	Night	4 5% 19% 44% 25% 3	630
	21st to end	Night	3 1 21% 44% 29% 3	630
July	1st to 10th	Night	4 2 13% 42% 37% 3	615
	11th to 20th	Night	3 1 8% 37% 44% 6%	612
	21st to end	Night	5% 1 7% 36% 43% 7%	690
August	1st to 10th	Night	3 1 8% 35% 44% 9%	627
	11th to 20th	Night	4 1 8% 42% 40% 4	624
	21st to end	Night	6% 2 8% 39% 40% 6%	693
September	1st to 10th	Night	5% 1 11% 42% 35% 5%	630
	11th to 20th	Night	5% 3 18% 40% 29% 5%	719
	21st to end	Night	8% 4 18% 37% 29% 5%	840
October	1st to 10th	Night	8% 8% 21% 37% 25% 2	840
	11th to 20th	Night	7% 4 24% 41% 21% 3	812
	21st to end	Night	6% 8% 23% 38% 21% 4	880
November	1st to 10th	Night	7% 3 23% 41% 21% 4	820
	11th to 20th	Night	6% 6% 27% 38% 19% 4	929
	21st to end	Night	12% 9% 24% 35% 17% 3	1050
December	1st to 10th	Night	11% 7% 24% 40% 16% 2	1050
	11th to 20th	Night	15% 6% 28% 34% 16% 1	1050
	21st to end	Night	15% 11% 26% 35% 12% 1	1081

Page generated at 2026-10-11 03:06:29. Version ac07

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